SEAMUS (v1.0): a Δ<sup>14</sup>C-enabled, single-specimen sediment accumulation simulator

Abstract

Abstract. The systematic bioturbation of single particles (such as foraminifera) within deep-sea sediment archives leads to the apparent smoothing of any temporal signal as record by the downcore, discrete-depth mean signal. This smoothing is the result of the systematic mixing of particles from a wide range of depositional ages into the same discrete depth interval. Previous sediment models that simulate bioturbation have specifically produced an output in the form of a downcore, discrete-depth mean signal. Palaeoceanographers analysing the distribution of single foraminifera specimens from sediment core intervals would be assisted by a model that specifically evaluates the effect of bioturbation upon single specimen populations. Taking advantage of recent increases in computer memory, the single-specimen SEdiment AccuMUlation Simulator (SEAMUS) was created in Matlab, whereby large arrays of single specimens are simulated. This simulation allows researchers to analyse the post-bioturbation age heterogeneity of single specimens contained within discrete-depth sediment core intervals, and how this heterogeneity is influenced by changes in sediment accumulation rate (SAR), bioturbation depth (BD) and species abundance. The simulation also assigns a realistic 14C activity to each specimen, by considering the dynamic Δ14C history of the Earth and temporal changes in reservoir age. This approach allows for the quantification of possible significant artefacts arising when 14C dating multi-specimen samples with heterogeneous 14C activity. Users may also assign additional desired carrier signals to specimens (e.g., stable isotopes, trace elements, temperature, etc.) and consider a second species with an independent abundance. Finally, the model can simulate a virtual palaeoceanographer by randomly picking whole specimens (whereby the user can set the percentage of older, broken specimens) of a prescribed sample size from discrete depths, after which virtual laboratory 14C dating and 14C calibration is carried out within the model.

Radiocarbon Dating of Small-sized Foraminifer Samples: Insights into Marine sediment Mixing

“…This ventilation and oxygenation history is consistent with enhanced bioturbation after HS1. Consequently, established understanding of bioturbation, combined with dynamic changes in benthic and planktonic foraminiferal abundances, help to explain the existence of negative 14 C B-P ages, as we show using a single foraminifera simulation (Lougheed 2020).…”

“…To further explore the potential of bioturbation to produce the negative 14 C B-P ages observed after HS1 on SU90-08 record, we created an idealized single foraminifera sediment archive simulation, using a single foraminifera sedimentation model developed by (Lougheed 2020). In order to construct an idealized modeling environment whereby as many variables as possible are kept constant, we considered a simple scenario with constant true ventilation ages and a uniform sediment mixed layer depth of 10 cm as well as idealized benthic and planktonic foraminifer abundances (Figure 7), so that we may use the model to quantify the influence of an isolated change in a single variable.…”

Modeling the impact of bioturbation and species abundance upon discrete-depth individual foraminifera analysis used in ENSO-type climate reconstructions.

“…Our modelling approach is carried out using an offline coupling of two transient models: a singleforaminifera sediment accumulation simulator (SEAMUS; (Lougheed, 2020)) run at a monthly timestep resolution, forced with monthly SST from the TRACE-21ka climate model (He, 2011). We investigate a number of best-case scenarios, concentrating on the time period spanning from 20 ka (BP 1950) up to and including 1989 CE, assuming a hypothetical sediment core at a location ideal for studying ENSO (Fig.…”

Re-evaluating <sup>14</sup>C dating accuracy in deep-sea sediment archives

“…The SEAMUS model (Lougheed, 2019) synthesises n number of single foraminifera raining down from the water column per simulation timestep, whereby n is the capacity of the synthetic sediment archive being simulated (analogous to core radius) scaled to the SAR of the timestep as predicted by an inputted age-depth relationship (Lougheed, 2019). To provide good statistics, all simulations use a timestep of 5 years and 10 4 synthetic foraminifera per cm core depth.…”

“…if it may ultimately lead to spurious downcore geochronological interpretations or not. To investigate for the presence of such artefacts, we employed the Δ 14 C-enabled, single-specimen SEdiment AccuMUlation Simulator (SEAMUS) (Lougheed, 2019). This model uses a similar understanding of bioturbation as included in existing bioturbation models (Trauth, 2013;Dolman and Laepple, 2018), but differs in that it explicitly simulates the accumulation and bioturbation of single foraminifera, each with individually assigned 14 C activities, to create a synthetic sediment archive history.…”